Termination of fiber optic cable

ABSTRACT

Apparatus and methods provide for cables with secured terminations. For some embodiments, a cable includes an inner tube surrounding an optical fiber, an aluminum tube surrounding the inner tube, and armor tubing surrounding the aluminum tube. The aluminum tube resists collapse of the inner tube at bends in the cable, inhibits or prevents hydrogen from reaching the fiber, and facilitates termination of the cable. For example, terminating the cable may include crimping the armor tubing to deform the aluminum tube into gripping engagement with an outside of the inner tube and an inside of the armor tubing. In some embodiments, a retention assembly secures the fiber relative to the inner tube and includes a retention tube secured to the inner tube and a packing sleeve squeezed into gripping engagement with the fiber by radial inward deformation of the retention tube where the packing sleeve is disposed in the retention tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 60/948,409, filed Jul. 6, 2007, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to cables, such asthose used in downhole operations.

2. Description of the Related Art

Cable represents a significant cost of downhole sensing systems. Costdrivers include materials, supplier yield issues, and associated testingcosts. Delays in cable build cycle time lead to increases in time neededfor delivery of the cable. Wasted cable also represents significant costsince there is often a significant amount of unused cable remnants(e.g., lengths less than 1500 meters) due to manufacturing defects.

Various such cost associated problems exist with prior cables, which mayutilize a polymer buffer between armor tubing and an inner tubingcarrying optical fibers. In addition, the polymer buffer can contributeto pinching of the inner tubing at bends in the cable and requiresremoval prior to welding onto the armor tubing. Termination of suchcables requires complicated and time consuming procedures.

Therefore, there exists a need for an improved cable and cabletermination.

SUMMARY OF THE INVENTION

In one embodiment, a method prepares a cable with a secured termination.The cable includes an inner tube having an optical fiber disposed insidethe inner tube. The method includes removing a portion of an inner tubeof the cable at an end of the cable to expose a length of the opticalfiber extending from an end of the inner tube, positioning anelastomeric packing sleeve surrounding at least part of the length ofthe optical fiber adjacent the end of the inner tube, positioning aretention tube overlapping outsides of both the inner tube and theelastomeric packing sleeve, and securing the retention tube to the innertube. In addition, deforming the retention tube in a radial inwarddirection where the packing sleeve is disposed in the retention tubesqueezes the packing sleeve into gripping engagement with the opticalfiber.

For one embodiment, a cable with a secured termination includes anoptical fiber and an inner tube surrounding the optical fiber with alength of the optical fiber extending from an end of the inner tube. Anelastomeric packing sleeve surrounds at least part of the length of theoptical fiber adjacent the end of the inner tube. Further, a retentiontube overlaps outsides of both the inner tube and the elastomericpacking sleeve, is secured to the inner tube, and is deformed in aradial inward direction where the packing sleeve is disposed in theretention tube to squeeze the packing sleeve into gripping engagementwith the optical fiber.

According to one embodiment, a method of preparing a cable with asecured termination utilizes the cable that includes an inner tubehaving an optical fiber disposed inside the inner tube, an aluminum tubesurrounding the inner tube and armor tubing surrounding the aluminumtube. Removing a portion of the armor tubing, the aluminum tube and theinner tube at an end of the cable exposes a length of the optical fiberextending from an end of the inner tube. Crimping a section of the armortubing secures the armor tubing, the aluminum tube and the inner tuberelative to one another. Securing the optical fiber relative to theinner tube occurs with a retention assembly coupled to the inner tubeand at least part of the length of the optical fiber adjacent the end ofthe inner tube.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a cross-section view of a cable with an aluminum tube disposedbetween armor tubing and an inner tube surrounding one or more opticalfibers, according to one embodiment.

FIG. 2 is a cross-section view of the cable taken across line 2-2 inFIG. 1 and along a curved length of the cable, according to oneembodiment.

FIG. 3 is a view of an end of the cable depicting one stage ofterminating of the cable with the inner tube, the aluminum tube and thearmor tubing cut and the armor tubing having been crimped, according toone embodiment.

FIG. 4 is a cross-section view of the cable taken across line 4-4 inFIG. 3 showing deformation of the armor tubing and hence the aluminumtube where crimped, according to one embodiment.

FIG. 5 is a view of the end of the cable showing sliding of one or moreelastomeric sleeves over the one or more fibers in a succeeding stage ofterminating of the cable, according to one embodiment.

FIG. 6 is a view of the end of the cable illustrating a subsequent stageof terminating of the cable with the one or more elastomeric sleeves inplace and sliding of a retention tube over the one or more elastomericsleeves and the inner tube, according to one embodiment.

FIG. 7 is a view of the end of the cable once termination is completedwith the retention tube crimped over the one or more elastomeric sleevesand crimped over the inner tube, according to one embodiment.

DETAILED DESCRIPTION

Apparatus and methods relate to cables that may have securedterminations. For some embodiments, a cable includes an inner tubesurrounding an optical fiber, an aluminum tube surrounding the innertube, and armor tubing surrounding the aluminum tube. The aluminum tuberesists collapse of the inner tube at bends in the cable, inhibits orprevents hydrogen from reaching the fiber, and facilitates terminationof the cable. For example, terminating the cable may include crimpingthe armor tubing to deform the aluminum tube into gripping engagementwith an outside of the inner tube and an inside of the armor tubing. Insome embodiments, a retention assembly secures the fiber relative to theinner tube and includes a retention tube secured to the inner tube and apacking sleeve squeezed into gripping engagement with the fiber byradial inward deformation of the retention tube where the packing sleeveis disposed in the retention tube.

FIG. 1 shows a cross-section view of a cable 100. The cable 100 includesthree optical fibers 102 disposed inside an inner tube 104. While threeare shown as an example, the inner tube 104 may contain any number ofthe optical fibers 102. In some embodiments, a filler material 106 isdisposed in the inner tube 104 and substantially fills the void spaceswithin the inner tube 104 surrounding the optical fibers 102 to supportand prevent the optical fibers 102 from moving excessively within theinner tube 104.

The filler material 106 has sufficient viscosity to resist the shearforces applied to it as a result of the weight of the optical fiber 102when disposed in a vertical well installation at elevated temperatures,thereby supporting the optical fibers 102 without subjecting the fibersto the strain of their weight. The filler material 106 allows theoptical fibers 102 to relax and straighten with respect to the innertube 104 due to differences in the coefficients of thermal expansionbetween the optical fiber 102 and the inner tube 104 and duringspooling, deployment and use of the cable 100. In addition, the fillermaterial 106 also prevents chaffing of the coatings on the opticalfibers 102 as a result of bending action during installation andvibration of the cable 100. The filler material 106 also serves as acushion for the optical fiber 102 against the surface of the inner tube104 to avoid microbend losses across cable bends. Suitable compounds forthe filler material 106 include conventional thixotropic gels or greasecompounds commonly used in the fiber optic cable industry for waterblocking, filling and lubrication of optical fiber cables.

The cable 100 further includes an aluminum tube 108 disposed around theinner tube 104 and within armor tubing 110 of the cable 100. For someembodiments, outer jacketing, such as a polymeric coating, surrounds thearmor tubing 110. The inner tube 104 and armor tubing 110 may bemanufactured of the same material, such as a metal or metal alloy.Examples of suitable materials include corrosion resistant metal alloyssuch as 304 stainless steel, 316 stainless steel, INCONEL® 625 andINCOLOY® 825.

The aluminum tube 108 substantially fills an annular area between theinner tube 104 and the armor tubing 110. In some embodiments, an outerdiameter of the inner tube 104 being about 0.1 to 0.3 mm smaller than aninner diameter of the aluminum tube 108 defines a first annular air gap107 and an outer diameter of the aluminum tube 108 being about 0.1 to0.3 mm smaller than an inner diameter of the armor tube 104 forms asecond annular air gap 109. In some embodiments, aluminum or an aluminumalloy forms the aluminum tube 108, which may also be made of othermetals or metal alloys that resist hydrogen diffusion and/or are moreductile than the inner tube 104 and armor tubing 110.

For some embodiments, manufacturing of the aluminum tube 108 byextrusion produces the aluminum tube 108 without any longitudinal seamsor welds. When extruded, the material forming the aluminum tube 108 isheated and pushed through a die. This extrusion may occur over the innertube 104. Compared to folding and welding to make the aluminum tube 108,the extrusion reduces costs and limits defects in the aluminum tube 108that can be caused by skips or pin holes occurring with welds. Thicknessselection for the aluminum tube 108 corresponds to level of hydrogenprotection provided by the aluminum tube 108 that blocks hydrogenoutside of the cable 100 from reaching the optical fibers 102.

The thickness of the aluminum tube 108 may provide equal or betterhydrogen protection than that provided by tin plating on the inner tube104 such that this plating process may not be required. The aluminumtube 108 also replaces polymer material disposed between the inner tube104 and the armor tubing 110. Eliminating the plating and polymermaterial reduces costs and avoids other problems. For example, the innertube 104 does not need to be shipped to a separate company and/orlocation for the plating that can require several days and cause breaksin length of the inner tube 104. Further, addition of the polymermaterial may occur at yet another company and/or location and alsointroduce yield problems.

The aluminum tube 108 further acts as a heat sink when desired to weldover the armor tubing 110 as may be required at terminations of thecable 100. The aluminum tube 108 thereby withstands heat caused bywelding while protecting the optical fibers 102 from the heat. This heatsink aspect provides additional cost advantages compared to designsutilizing the polymeric material instead of the aluminum tube 108. Forexample, welding processes for use with the designs having the polymericmaterial require coring out of the polymeric material and replacing thepolymeric material with a copper heat sink where welding is desired. Thewelding must then occur at this particular location in order to avoidcable damage.

To further reduce the effects of hydrogen on the optical fibers 102, thefiller material 106 may optionally include or be impregnated with ahydrogen absorbing/scavenging material, such as palladium or tantalum.In one embodiment, the hydrogen absorbing/scavenging material is avanadium-titanium wire coated with palladium. For some embodiments, theinner tube 104 may be coated and/or impregnated with a hydrogenabsorbing/scavenging material.

FIG. 2 illustrates a cross-section view of the cable 100 taken acrossline 2-2 in FIG. 1 and along a curved length of the cable 100. Thealuminum tube 108 keeps the inner tube 104 substantially centered withinthe armor tubing 110 so as to maintain a common length relationshipbetween each when rolled onto a drum. Bending of the cable 100 by aboutninety degrees often occurs at a tree flange or wellhead of a well. Insuch a bend, the aluminum tube 108 improves resistance to collapse ofthe inner tubing 104 compared to designs utilizing the polymericmaterial. By acting as a mechanical support structure, the aluminum tube108 achieves a smooth bend transition without permitting breakage orstress damage to the optical fibers 102 due to collapse and kinking ofthe inner tube 104.

FIG. 3 shows an end of the cable 100 depicting one stage of terminatingof the cable 100. Terminating the cable 100 permits repairing a damagedsection of the cable 100, coupling the cable 100 to an optical sensor orsurface equipment, or adding an additional cable length. However,shifting of components in the cable 100 relative to each other due totensile loads or thermal expansion can damage the optical fibers 102that extend from the end of the cable 100. Secured termination at theend of the cable 100 prevents such relative movement. In operation,preparing a termination for the cable 100 begins by cutting the armortubing 110, the aluminum tube 108, and then the inner tube 104 andforming crimps 300 in the armor tubing 110.

With respect to the cutting, a portion of the armor tubing 110 is firstremoved from the end of the cable 100. The operator can use a standardtube cutter to score the outside of the armor tubing 110, which theoperator can then file and/or flex at the score to cleave the portion ofthe armor tubing 110 being stripped. A sufficient length (e.g. fiftycentimeters) of the armor tubing 110 is stripped from the end of thecable 100 in order to leave enough of the optical fibers 102 to form anydesired couplings at free ends of the optical fibers 102. Next, aportion of the aluminum tube 108 is stripped from the cable 100. While alength of the aluminum tube 108 is shown extending past the armor tubing110 to facilitate ease of cutting the aluminum tube 108, the aluminumtube 108 may be stripped such that the aluminum tube 108 and the armortubing 110 are flush or coterminous. The operator can use the standardtube cutter to cut through most of the aluminum tube 108 prior totwisting and sliding off the end of the cable 100 the portion of thealuminum tubing 108 being stripped. Once the portion of the aluminumtube 108 is removed, the operator can score the inner tube 104 with aknife file and flex the inner tube 104 to cleave a portion of the innertube 104 being stripped. The inner tube 104 is stripped such that alength (e.g. four millimeters) of the inner tube 104 extends past thealuminum tube 108.

Mechanical crimps 300 secure the inner tube 104 to the armor tubing 110via the aluminum tube 108. In particular, the crimps 300 deform thealuminum tube 108 into gripping engagement with an outside surface ofthe inner tube 104 and an inside surface of the armor tubing 110. Whileroller crimping may be used to perform the crimping, this time consumingand more sensitive procedure may not be required. Thus, a crimping toolhaving die inserts can be used to provide the crimps 300. Depending onthe shape of the die inserts of the crimping tool, the crimps 300 may bea hex crimp, a circular crimp, or any other shape. While three of thecrimps 300 are shown positioned along the outside of the armor tubing110, any number of the crimps 300 may be used in succession to create astronger holding force between the inner tube 104 and the armor tubing110.

FIG. 4 illustrates a cross-section view of the cable 100 taken acrossline 4-4 in FIG. 3 showing deformation of the armor tubing 110 and hencethe aluminum tube 108 where crimped. Forming two of the crimps 300simultaneously facilitates in filling in between the crimps 300 that arecreated at the same time with the material of the aluminum tube 108 tocreate a seal between the inner tube 104 and the armor tubing 110. Forsome embodiments, the die inserts of the crimping tool thus include oneor more corresponding hollowed out mid-regions to enable forming thecrimps 300 at spaced apart locations. Unlike one continuous crimpequivalent in size to a combined area of the crimps 300, the crimps 300at multiples spaced locations gives the material of the aluminum tube108 a place to be displaced. This spacing of the crimps 300 avoidscreating excessive forces on the inner tube 104 that tend to crush theinner tube 104 given that displacement of the material of the aluminumtube 108 must otherwise go somewhere.

FIG. 5 shows the end of the cable 100 in a succeeding stage ofterminating of the cable 100. A first movement arrow 501 depicts slidingover the fibers 102 of a tubular protective insert 502 and a tubularbody 500 that may both be coupled together prior to being positionedonto the cable 100. A second movement arrow 503 represents subsequentsliding of an optional elastomeric packing sleeve 504 over the fibers102. For some embodiments, the body 500 is integrated with or otherwiseserves the functions described herein with respect to the elastomericpacking sleeve 504.

In some embodiments, a portion of the protective insert 502 is disposedconcentric within the body 500 while a remainder of the protectiveinsert 502 extends beyond an end of the body 500. The protective insert502 may, for example, be made of a polymer such as polyimide. For someembodiments, the body 500 is made of a polymer or elastomer such assilicone. In order to position the body 500 and the protective insert502 on the end of the cable 100, the fibers 102 are run through innerbores of the protective tube 502 and the body 500. The portion of theprotective insert 502 that extends beyond the body 500 inserts into theinner diameter of the inner tube 104. In this manner, the protectiveinsert 502 protects the fibers 102 from any burrs on the end of theinner tube 104 along where the inner tube 104 was cut. As an outerdiameter of the body 500 is greater than an outer diameter of theprotective tube 502 and the inner diameter of the inner tube 104, thebody 500 abuts against the cut end of the inner tube 104.

An elastomer material, such as silicone, forms the elastomeric packingsleeve 504 that is then positioned on the cable 100 against the body 500by running the fibers 102 through an inner bore of the packing sleeve504. The packing sleeve 504 can have a greater wall thickness and asmaller inner diameter than the body 500 given that the body 500 may bedesigned with an inner diameter sufficient to receive the protectiveinsert 502. Since ability of the packing sleeve 504 to grip the fibers102 as described further herein depends on these dimensional features,the packing sleeve 504, by being a separate component, can bedimensioned with ease and as desired independent of any criteriaassociated with the body 500.

FIG. 6 illustrates the end of the cable 100 after the protective insert502, body 500, and packing sleeve 504 have been positioned on the cable100. In a subsequent stage of terminating of the cable 100, a thirdmovement arrow 601 depicts sliding of a retention tube 600 onto thecable 100 to position the retention tube 600 over the packing sleeve 504and the inner tube 104. A stainless steel or other metal or metal alloymay form the retention tube 600. The retention tube 600 may abut thealuminum tube 108 when located on the cable 100. For some embodiments,preassembly of two or more of the protective insert 502, body 500,packing sleeve 504 and retention tube 600 may occur prior to positioningof such a subassembly on the cable 100.

FIG. 7 shows the end of the cable 100 once termination is completed. Afirst crimp 700 made to the retention tube 600 and located where thepacking sleeve 504 is disposed in the retention tube 600 connects thepacking sleeve 504 and the retention tube 600 together. Further, thefirst crimp 700 deforms the retention tube 600 in a radial inwarddirection and hence squeezes the packing sleeve 504 around the fibers102 such that the packing sleeve 504 grips the fibers 102 and/or sealsagainst the fibers 102. A second crimp 701 connects the retention tube600 to the inner tube 104 by crimping the retention tube 600 against theinner tube 104 located beneath the retention tube 600 at a location ofthe second crimp 701.

As a result of the termination, components of the cable 100 areprevented from moving relative to one another given thermal expansioneffects and tensile or mechanical forces, such as bending and weight.The termination thereby holds all components of the cable 100 to avoidmovement of the fibers 102 at, for example, splices. A force of 95pounds may be put on the termination from the aluminum tube 108 whenraising the temperature to 175° C. Therefore, cable termination tensileload specifications of 200 pounds hold the thermal expansion forces.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method of preparing a cable with a secured termination, comprising:providing the cable comprising an inner tube having an optical fiberdisposed inside the inner tube; removing a portion of the inner tube atan end of the cable to expose a length of the optical fiber extendingfrom an end of the inner tube; positioning an elastomeric packing sleevesurrounding at least part of the length of the optical fiber adjacentthe end of the inner tube; positioning a retention tube overlappingoutsides of both the inner tube and the elastomeric packing sleeve;securing the retention tube to the inner tube; and deforming theretention tube in a radial inward direction where the packing sleeve isdisposed in the retention tube to squeeze the packing sleeve intogripping engagement with the optical fiber.
 2. The method of claim 1,wherein securing the retention tube to the inner tube includes crimpingthe retention tube against the outside of the inner tube.
 3. The methodof claim 1, further comprising crimping a section of armor tubing tosecure the armor tubing, an aluminum tube and the inner tube relative toone another, wherein the cable further comprises the aluminum tubesurrounding the inner tube and the armor tubing surrounding the aluminumtube.
 4. The method of claim 1, wherein the elastomeric packing sleevecomprises silicone.
 5. The method of claim 1, further comprisingpositioning a tubular protective insert into the end of the inner tube.6. The method of claim 1, further comprising positioning a first end ofa tubular protective insert into the end of the inner tube, wherein asecond end of the insert is received in a body that is adjacent the endof the inner tube and has a larger outer diameter than the insert.
 7. Acable with a secured termination, comprising: an optical fiber; an innertube surrounding the optical fiber, wherein a length of the opticalfiber extends from an end of the inner tube; an elastomeric packingsleeve surrounding at least part of the length of the optical fiberadjacent the end of the inner tube; and a retention tube overlappingoutsides of both the inner tube and the elastomeric packing sleeve,wherein the retention tube is secured to the inner tube and theretention tube is deformed in a radial inward direction where thepacking sleeve is disposed in the retention tube to squeeze the packingsleeve into gripping engagement with the optical fiber.
 8. The cable ofclaim 7, wherein the elastomeric packing sleeve comprises silicone. 9.The cable of claim 7, further comprising: an aluminum tube surroundingthe inner tube; and armor tubing surrounding the aluminum tube, whereina section of the armor tubing is crimped to secure the armor tubing, thealuminum tube and the inner tube relative to one another.
 10. The cableof claim 7, wherein the aluminum tube is formed of extruded material andis thereby seamless.
 11. The cable of claim 7, wherein the retentiontube is secured to the inner tube by a crimp in the retention tube thatpresses the retention tube against the outside of the inner tube. 12.The cable of claim 7, wherein the inner tube and the retention tube areboth made of metallic material.
 13. The cable of claim 7, furthercomprising: a metal tube surrounding the inner tube; and armor tubingsurrounding the metal tube and crimped to secure the armor tubing, themetal tube and the inner tube relative to one another, wherein the metaltube is made of a material more ductile than the inner tube and thearmor tubing.
 14. The cable of claim 7, further comprising: a metal tubesurrounding the inner tube; and armor tubing surrounding the metal tubeand crimped to secure the armor tubing, the metal tube and the innertube relative to one another, wherein the metal tube is made of amaterial more impermeable to hydrogen than the inner tube and the armortubing.